Mod Con Constant Circulation Piping

TeddyHertel · December 2023

Hi, first post but have read a ton of info on here, thank you for all of the knowledge. I have read cover to cover John's Modern Hydronic book so hopefully I'm not a broken record on here. I'm building a house for myself in Northern California and am about to start the radiant system. I have a few questions. First a bit of background.

House is 2400 sqft, all up to new Title 24 code insulation, etc. Building heat loss is 32 kbtu on design day (28 degrees F). Radiant panel is Ecowarm (warmboard type system) with above subfloor aluminum panels (12" OC 1/2" pex with around 200' loops). Total of three radiant zones but going to run single supply temp for all (around 104F for 68-70F room temps if my calcs are correct), with DHW priority to a indirect tank. I got a Lochinvar Knight WHB 055 which is about the smallest I could find that would fit this scenario.

My plan is to run continuous circulation with TRV's on all (or all but one) of the zones with ODR and probably a WWSD. Planning on using an Alpha pump for the system circ. I guess what I'm getting hung up on is the need for P/S or to just direct pipe to get the efficiency benefits. The Lochinvar manual has a schematic for both ways to pipe it but I'm not sure which to go with. The radiant loops for the three zones all meet the minimum boiler flow (1.0 gpm) so i figure if i leave one without a TRV and run it constant circ i shouldn't have a problem with the boiler Hx? Would be nice to cut out one P/S circ (boiler circ) if i can (we are off-grid solar). Any help is appreciated, I will update with pictures. Attached the two piping methods below. Thanks in advance.

hot_rod · December 2023

Is it a Lochinvar Knight? They ship with a variable speed circ that the boiler control modulates to maximize efficiency. So you would want to pipe it with a hydraulic sep to use an Alpha on the radiators with TRVs

EdTheHeaterMan · December 2023

TRVs are a dfferent idea for controlling radiant zones. Are you going to use the valve actuator that has the remote (capillary tube) sensor? Where are you going to mount the sensor and where is the actual valve going to be. I'm trying to picture this in my mind. The valve needs to be on the manifold that feeds all the loops for that zone, and the sensor needs to be in the space in order to get a good temperature sample. How long are the cap tubes on the remote sensors?

Then there is the decision of which zone is the one that needs to be open all the time? It should be on the zone that is hardest to heat... but how do you know what zone that is until you actually try to heat the zones? What if you select the wrong zone and the other two TRVs are always open trying to catch up to the the zone that is always much too warm so the boiler shuts off. You really need do think about this. You know I would recommend... Do It Right or don't do it at all!

Off grid solar... so I can appreciate wanting to be as electric free as possible... so no electric zone valves... What happens if you have several weeks of no sun as a result of weather or perhaps smoke from those famous California wildfires. Will you have a generator backup?

hot_rod · December 2023

The Oventrop uni box is a nice control for radiant TRV control

Derheatmeister · December 2023

hot_rod said:
Is it a Lochinvar Knight? They ship with a variable speed circ that the boiler control modulates to maximize efficiency. So you would want to pipe it with a hydraulic sep to use an Alpha on the radiators with TRVs

We have never seen the Lochinvar 55.000 BTU shipped with a variable speed...A couple years ago the medium sized knights >>>USED <<<to ship with the OEM Grundfos variable speed circ but currently they come with a regular 15-58 for the 55/85/110/or a regular 26-99 for the larger models.

Derheatmeister · December 2023

EdTheHeaterMan said:
TRVs are a dfferent idea for controlling radiant zones. Are you going to use the valve actuator that has the remote (capillary tube) sensor? Where are you going to mount the sensor and where is the actual valve going to be. I'm trying to picture this in my mind. The valve needs to be on the manifold that feeds all the loops for that zone, and the sensor needs to be in the space in order to get a good temperature sample. How long are the cap tubes on the remote sensors?

Then there is the decision of which zone is the one that needs to be open all the time? It should be on the zone that is hardest to heat... but how do you know what zone that is until you actually try to heat the zones? What if you select the wrong zone and the other two TRVs are always open trying to catch up to the the zone that is always much too warm so the boiler shuts off. You really need do think about this. You know I would recommend... Do It Right or don't do it at all!

Off grid solar... so I can appreciate wanting to be as electric free as possible... so no electric zone valves... What happens if you have several weeks of no sun as a result of weather or perhaps smoke from those famous California wildfires. Will you have a generator backup?

We have done entire homes using TRV'S ...This is regularly used in Europe but heavily miss understood in the US.
The longest length on the capillary tubes that we know of is 33 feet so installation of manifold should be within this distance
"Smurf Tubing" should be used as a conduit for a possible replacement of the TRV in the future.

BTW Very wise German mentors used to teach :If your heating curve which is based on Outdoor reset is adjusted ever so slightly above the curve (Heating requirements of the home ) the TRV'S act as a Restrictor of the heat not a activator..
On my last stay in a Rented home in Germany the Viessmann 222 just turned on in the fall and will probably >>> modulate <<< the boiler and the TRV'S all winter based on the outdoor/indoor conditions.. Very efficient.

TeddyHertel · December 2023

Thanks for all the prompt feedback!

hot_rod said:
Is it a Lochinvar Knight? They ship with a variable speed circ that the boiler control modulates to maximize efficiency. So you would want to pipe it with a hydraulic sep to use an Alpha on the radiators with TRVs

It is a Lochinvar Knight boiler, shipped with a Grundfos 15-58 pump. Makes me think a hydraulic sep is necessary with the Alpha circulating the zones? Or swap out the 15-58 for the Alpha? Luckily the Knight has quite a few logic options for controlling pumps. As far a TRV's I was looking at Danfoss with the capilary tubing run to the rooms that the TRV controls. Using Caleffi manifolds that the TRV would be located next to. The Unibox looks like it could be a good option too.

As far as the solar system, we have plenty of power, backup gen, etc. I was just trying to limit the number of pumps to keep things simple more than save power (less pumps to replace in the future). We set the system up after the utility company gave us an outrageous quote for a power drop and then the power was out for a week due to fires. Now when the powers out (fires in the summer, storms in the winter), we're the only ones in town with the lights on. Solar tech has come so far and is now affordable, I highly recommend it.

My bottom line is I'm really trying to keep the system as slick and simple as possible. We don't care about internet-connected thermostats, not planning on changing the room temp ever if possible, set it and forget it. The less I think about the system once it's tuned the better. My thought was to direct pipe with the boiler (since it seems possible on the Knight) and run constant circ with TRV (and capillary tubes). Just want to make sure I'm on the right track. Thank you all

EBEBRATT-Ed · December 2023

With any boiler especially a small water content volume my theory is you want to keep the HX happ. That IS the boiler.

That being said I would go primary secondary all the time JMHO. Lack of flow, minimum flow scares me with low water content. Why risk overheating the HX?

Derheatmeister · December 2023

If your heat loos is correct you could also install a Viessmann 3UCA-94...
This boiler has a High mass/large fluid volume content which acts as a buffer tank,It Modulates down to 19.000 BTU/HR and does not require a additional circ.

As with any offgrid we highly recommend installing a UPS to protect the boiler from voltage spikes
https://www.viessmann-us.com/en/products/vitocrossal/vitocrossal-300-cu3a.html

Hot_water_fan · December 2023

I like the high mass condensing boilers like the Viessmann for their lack of circulator needs too. It’s like using a domestic tank water heater as a boiler but more efficient and actually designed for central heating

TeddyHertel · December 2023

Well seeing as I already have the Knight boiler in my mech room I’m going with it. I guess P/S piping it is to keep the boiler happy. Next question is to put TRVs on all the zones or leave one free flow?

Derheatmeister · December 2023

TeddyHertel said:
Well seeing as I already have the Knight boiler in my mech room I’m going with it. I guess P/S piping it is to keep the boiler happy. Next question is to put TRVs on all the zones or leave one free flow?

Ohhh... I did not know that you had allready purchased the boiler.
Even thougth you should be able to adjust the way the Lochinvar reacts on a call for heat with the Out Door Sensor/WWSD,Supply sensor,Ramp delay,Modulation Factor Based on the size of the boiler and the heatloos i would recommend a Buffertank such as the Boiler Buddy..This will act as a hydronic seperator/air sep/dirt sep./and a buffer tank.
Personally i would go with TRV's/Alpha setup on the distribution side.

hot_rod · December 2023

Derheatmeister said:

hot_rod said:
Is it a Lochinvar Knight? They ship with a variable speed circ that the boiler control modulates to maximize efficiency. So you would want to pipe it with a hydraulic sep to use an Alpha on the radiators with TRVs
We have never seen the Lochinvar 55.000 BTU shipped with a variable speed...A couple years ago the medium sized knights >>>USED <<<to ship with the OEM Grundfos variable speed circ but currently they come with a regular 15-58 for the 55/85/110/or a regular 26-99 for the larger models.</p>

The one in my shop came with the VS pump, 3 years ago. Was it an option?

Derheatmeister · December 2023

hot_rod said:

Derheatmeister said:

hot_rod said:
Is it a Lochinvar Knight? They ship with a variable speed circ that the boiler control modulates to maximize efficiency. So you would want to pipe it with a hydraulic sep to use an Alpha on the radiators with TRVs
We have never seen the Lochinvar 55.000 BTU shipped with a variable speed...A couple years ago the medium sized knights >>>USED <<<to ship with the OEM Grundfos variable speed circ but currently they come with a regular 15-58 for the 55/85/110/or a regular 26-99 for the larger models.</p>
The one in my shop came with the VS pump, 3 years ago. Was it an option?

No it was not an option...Thgey came with variable speed for about two years then i guess due to availbility or cost the reverted bback to the regular 15-58 or the 26-99 Circulating pumps.

hot_rod · December 2023

Derheatmeister said:

hot_rod said:

Derheatmeister said:

hot_rod said:
Is it a Lochinvar Knight? They ship with a variable speed circ that the boiler control modulates to maximize efficiency. So you would want to pipe it with a hydraulic sep to use an Alpha on the radiators with TRVs
We have never seen the Lochinvar 55.000 BTU shipped with a variable speed...A couple years ago the medium sized knights >>>USED <<<to ship with the OEM Grundfos variable speed circ but currently they come with a regular 15-58 for the 55/85/110/or a regular 26-99 for the larger models.</p>
The one in my shop came with the VS pump, 3 years ago. Was it an option?

No it was not an option...Thgey came with variable speed for about two years then i guess due to availbility or cost the reverted bback to the regular 15-58 or the 26-99 Circulating pumps.

Actually, in some cases it limits output by trying to keep it condensing, or efficient. Never made a lot of sense, like most ∆T circ applications

TeddyHertel · December 2023

I'm still on the fence about P/S versus direct piping. The Knight manual shows it piped both ways, see the direct piping:

I am using TRVs instead of zone valves, but same idea. I also need to double check the boiler pump that came with it, I might have been mistaken and it is variable speed. in that case seems like just follow the manual and direct pipe, leave one zone without TRV to ensure min flows?

TeddyHertel · December 2023

heres the P/S for comparison:

Let me know what y'all think. Thanks!

hot_rod · December 2023

As long as you can assure the required flow that they ask for you can direct pipe.

P/S is a method that assures the boiler always has the required flow. It requires an additional pump and you will get some temperature blending, in the closely spaced tees.

Delta P circs work great with TRV systems.

ScottSecor · December 2023

With the low water content boiler I would be reluctant with TRV systems. I think there is a chance the boiler could fire with no flow through the thermostatic valves, could be a problem. I guess you could include a permanent bypass (maybe half inch pipe would do it?). We much prefer P/S piping or H/S if dealing with more than one zone (almost every system we see has multiple zones).

Derheatmeister · December 2023

TeddyHertel said:
I'm still on the fence about P/S versus direct piping. The Knight manual shows it piped both ways, see the direct piping:

I am using TRVs instead of zone valves, but same idea. I also need to double check the boiler pump that came with it, I might have been mistaken and it is variable speed. in that case seems like just follow the manual and direct pipe, leave one zone without TRV to ensure min flows?

As long as you can asure the minimum flowrates are sadisfied you can pipe it direct without a LLH/Buffer tank or closely spaced tees(P/S)
BTW...TRVs are not the same as Zonevalves when it comes to flow...They open proportional depending on heat requiremnets and may just "Sip" some heat into the heat emission surfaces/Rads.... So be careful !

TeddyHertel · March 8

Hi all, back with updates. Got the system installed and running. Works great! Lochinvar Knight WH055 with Danfos trv’s on all three zones, Alpha 15-58 system circ that is set to proportional pressure. Slowly dialing the ODR curve which is nice because it’s about the coldest days of the year here right now (coastal N CA). My only hang up is that I think the boiler circulator is running too fast. I ended up piping P/S with close tees, alpha on the secondary side and the Grundfos 3 speed circulator that came with the boiler on the primary loop. I have it set to the lowest speed but I’m seeing really small delta T in the boiler (5-10 degrees). Maybe this isn’t a problem I’m not sure, just have read cooler return temps help efficiency. My delta T on the radiant (warm board) loops are around 12-20. Also with the way I have it set now the boiler runs almost all night at about 20% modulation and then cycles a few times in the day depending on the weather. What is the ideal run time for the mod-con boiler? Constant or a few cycles a day or? The Alpha runs constantly so I guess I’ve achieved constant circulation? Any advice is appreciated. Thanks

Hilly · March 10

The knight pump has the tick box when purchasing. I have seen them with all the options. I think it really depends who orders if you get a 3-spd or VS grundfos.

hot_rod · March 10

I bought my knight 4 years ago, it came with a VS circ. Ive heard they went back to fixed speed

It may depend on the date code on the boiler
The pump will say VS and have 4 wires

Derheatmeister · March 10

TeddyHertel said:
Hi all, back with updates. Got the system installed and running. Works great! Lochinvar Knight WH055 with Danfos trv’s on all three zones, Alpha 15-58 system circ that is set to proportional pressure. Slowly dialing the ODR curve which is nice because it’s about the coldest days of the year here right now (coastal N CA). My only hang up is that I think the boiler circulator is running too fast. I ended up piping P/S with close tees, alpha on the secondary side and the Grundfos 3 speed circulator that came with the boiler on the primary loop. I have it set to the lowest speed but I’m seeing really small delta T in the boiler (5-10 degrees). Maybe this isn’t a problem I’m not sure, just have read cooler return temps help efficiency. My delta T on the radiant (warm board) loops are around 12-20. Also with the way I have it set now the boiler runs almost all night at about 20% modulation and then cycles a few times in the day depending on the weather. What is the ideal run time for the mod-con boiler? Constant or a few cycles a day or? The Alpha runs constantly so I guess I’ve achieved constant circulation? Any advice is appreciated. Thanks

A few cycles per day is okay.
Our boiler purrs like a kitten when it is warm outside and ramps up when it is cold outside.
It can take multipal attempts to find the perfect settings on a Modcon setup.
On the Lochinvar a couple come to mind.
1. Turn on the Ramp Delay.
2. Adjust all 6 Ramp Mod % and times
3. Adjust the >>MOD FACTOR<<
4. Adjust your Flowrates for each loop/Rads based on a good Delta T
5. Adjust your Flowrates for the circs. i.e Proportional pressure 1,2 or 3
As for the MOD FACTOR which is not to be confused by the modulation in the ramp delay: I am not sure if this parameter is available without the ConXus interface ?
The Mod factor will allow the boiler to respond faster or slower which in turn will help to prevent shortcycling.
Edit...To answer your question regarding the most ideal run times:
1. A boiler that does not operate at all is most efficient....LOL
2. IMO a boiler that operates from the fall to the spring on constant flow and modulating base on ODR at all times is most efficient and desired...
Since your system has modulating TRV's,a boiler that will modulate based on the outdoor temperature and a modulating circulating pump you should be able to achieve this.
Take your time and Have fun finding that sweet spot.

TeddyHertel · March 12

Thanks for the feedback. Slowly dialing in the boiler to modulate on the ODR. Ramp delay really helps smooth things out. I will say the Knight is an awesome machine, so many settings, great controls. Now I’m wondering if my system (secondary) pump is too small. It’s an Alpha 15-58 set on auto adapt proportional pressure. It says it’s moving about 2-2.5 gpm but I’m not sure I trust that measurement. I have 9 200’ 1/2 pex loops, three manifolds, one of which is on a second story. I think I calc’d about 3.5 gpm for the radiant loops. I already figured I would be at the upper end of the 15-58 range but I’m wondering if an Alpha 22-99 would be better suited? I would be at the very low end of that pump but I think my small delta T at the boiler (5-10 degrees) is from the undersized pump and I’m just recycling boiler water. Any thoughts? I’ll try to dig up my flow calca. Thanks!

nosirra1Arrison · March 12

Try taking the Alpha off AutoAdapt. Set it to proportional pressure setting two or three (right hand indicator lights). AutoAdapt rarely provides enough flow. That should give you a better delta T through the boiler. The Alpha 15-58 should be plenty of pump.

TeddyHertel · March 12

Ok thanks, I’ll switch the settings and let you know.

Derheatmeister · March 12

TeddyHertel said:
Thanks for the feedback. Slowly dialing in the boiler to modulate on the ODR. Ramp delay really helps smooth things out. I will say the Knight is an awesome machine, so many settings, great controls. Now I’m wondering if my system (secondary) pump is too small. It’s an Alpha 15-58 set on auto adapt proportional pressure. It says it’s moving about 2-2.5 gpm but I’m not sure I trust that measurement. I have 9 200’ 1/2 pex loops, three manifolds, one of which is on a second story. I think I calc’d about 3.5 gpm for the radiant loops. I already figured I would be at the upper end of the 15-58 range but I’m wondering if an Alpha 22-99 would be better suited? I would be at the very low end of that pump but I think my small delta T at the boiler (5-10 degrees) is from the undersized pump and I’m just recycling boiler water. Any thoughts? I’ll try to dig up my flow calca. Thanks!

Do you have flowsetters/ Visual flow indicators to each loop and do you adjust each loop for optimum delta T ?

TeddyHertel · March 13

Yeah they’re Caleffi manifolds with flow meters and flow valves (amongst other features). So far all of the manifolds seem to be running at or less than 1/4 gpm according to those flow meters. I’ve balanced them to set the flow about the same through all the loops (though they’re all about equal lenght). My calcs say I should be getting 1/3-1/2 gpm that’s why I thought the pump was undersized.

Mod Con Constant Circulation Piping

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